The following is a tabulation of some prior art that presently appears relevant:
U.S. Pat. Nos.U.S. Pat. Nos.Kind CodeIssue DatePatentee6,455,850B12002-9-24Coates6,452,179B12002-9-17Coates5,408,3061995-4-18Anderson
Emission spectroscopy is based on re-emission of the energy absorbed by an atom from an excitation process. Once an atom of an element is excited by a form of energy, its atomic structure is distorted to an unstable state, just as a compression-coil spring is compressed by force. The unstable state cannot be held, just as the compressed spring tends to recover to its relaxed state. When the spring bounces back to its relaxed state, mechanical energy stored by the spring is released. So do the excited atoms, but for atoms, the energy stored in their atomic structure is released by emitting light. Because each element has a unique atomic structure, its emission spectrum is uniquely related to its atomic structure, that is, it emits light only at certain wavelengths, called characteristic wavelengths of the element. For example, one of the characteristic wavelengths of copper is 324.75 nm (nanometer). If a peak of the light emitted by a sample appears at 324.75 nm, it is a positive identification of the existence of copper in the sample. On the other hand, the concentration of an element in a sample is proportional to the intensity (peak height) of the light emitted at the characteristic wavelengths. Thus Emission spectroscopy provides a means for knowing the existence and quantity of the element in the sample. The advantage of emission spectroscopy is that plural elements simultaneously emit light upon excitation, and thus the existence and concentration of the plural elements in a sample can be determined by a single excitation process.
A plurality of forms of energy can be used to excite atoms. One form of the energy is heat or high temperature plasma. Electric spark can provide the heat. Spark can be generated by applying a high voltage to a spark gap consisting of two electrodes. Sample is presented to the spark gap for excitation, which, in turn, produces emission spectra of elements in the sample. Laser is another approach to provide the heat. Once a pulsed laser beam is directed at a sample, a spot of the sample is heated by laser power to give emission spectra, which is called Laser Induced Breakdown Spectroscopy (LIBS). Another form of the energy is X-ray. Once an X-ray beam strikes a sample, the atoms in the sample are excited to produce an emission spectrum, called X-Ray Fluorescence (XRF) spectrum.
A typical apparatus of emission spectroscopy comprises an excitation site, where excitation energy is exposed to a sample, an excitation source for generating the energy, and a spectrometer for collecting the light emitted from the excitation site. The spectrometer is an apparatus that sorts light by wavelengths and measure the intensity of the light at any given characteristic wavelengths. Thus the information required for knowing the existence and quantity of any elements in the sample is both provided by the spectrometer.
Oil analysis provides information of wear occurred inside a compartment of mechanical equipment. If mechanical equipment is serviced by lubricant oil, the elements worn off from a moving part, such as a gear, may enter the oil in the form of metal particles. By analyzing the elemental types of the wear metals and their quantities, the internal conditions of the equipment and the degree of wear can be learned without having to disassemble it for a visual inspection. Thus oil analysis tells what the wear metals are, e.g., iron, aluminum, copper, and so on, and how much they are. For oil analysis, emission spectroscopy is a preferred tool because of its capacity of analyzing multi-elements in used oil by a single excitation.
Non-homogeneity is a problem for used-oil samples containing wear metals. Wear metals are not entirely dissolved in oil but exist in the form of particles with various sizes. These particles are suspended in the sample. But the suspension is not even. For example, large particles can quickly settle down to the bottom of a sample bottle while fine particles may stay everywhere in the bottle. As a result, at the bottom part of the bottle, the concentration of a wear metal is higher than that at the upper part. On the other hand, the existence of larges particles often reveals the events of severe wear or damage, while that of fine particles often results from chronically normal wear. Because the existence of large particles of wear metals may be evaluated as a precursor of a potential catastrophic failure for mechanical equipment, capturing and detecting the large particles is always an object of method development for oil analysis.
When reviewing the related art, two questions are in consideration. Firstly, whether the large particles can be captured and presented to the excitation site of an apparatus for producing emission? Secondarily, if the large particles can be captured and presented to the excitation site, whether their existence can be recognized? To understand the second question, consider this scenario, if a sample does not contain many fine particles but just a few of large particles, the overall concentration of corresponding wear metals is still low, not high enough to trigger a warning, because the strong emission signal from the large particles is averaged by overall weak emission signal. Thus the existence of large particles may not be recognized.
The most conventional method for exciting an oil sample is spark. However, because the electrode forming a spark gap has a limited cross-sectional area for holding the sample, continuously flowing of the sample to the tip of the electrode has to be maintained.
One approach to transport the oil sample to the spark gap is to configure the lower electrode of the spark gap into a wheel, called Rotating Disk Electrode (RDE), as described by U.S. Pat. No. 5,408,306 issued to Anderson on Apr. 18, 1995. The rotating disk is mounted vertically against a small sample container, with its lower part submerging into the sample fluid. The fluid contacts the disk and films on the disk circumference. The top part of the click forms the spark gap with an upper electrode. The vertical rotation of the disk brings the fluid-filmed circumference up to be exposed to the upper electrode of the spark gap. Continuous rotation is maintained during excitation and thus the fluid from the sample container is continuously fed to the spark gap. This approach is called conventional RDE analysis.
Another approach to transport the oil sample is to force it to flow into a spark gap, as disclosed by U.S. Pat. No. 6,455,850 B1 issued to Coates on Sep. 24, 2002. In this mechanism, the lower electrode of the spark gap is configured as an outlet of a fluid supplying conduit. The inlet of the fluid conduit is inserted into a sample bottle. A pump is used to mobilize the fluid through the fluid conduit and forces the fluid to flow through a through-bore portion of the lower electrode. Thus the fluid can continuously enter the spark gap.
The common feature of the two approaches is to provide a continuous flow of fluid for transporting a sample to a spark gap. The approaches solve the problem of sample supply for the spark gap, but cannot capture particles with the size greater than 0.03 mm and present them to the spark gap. The reason is simple: if a particle cannot be suspended by a fluid, it cannot flow with the fluid, such as river water cannot carry or move large stones to down stream because of the gravity of the stone.
For capturing large particles of wear metals, another approach with the RDE is also disclosed by the same U.S. Pat. No. 5,408,306. In summary, this approach captures the large particles from a sample by using a filter, and then analyzes the captured large particles independently. Then the same sample is analyzed by conventional RDE analysis, in which the large particles are absent. This approach provides a way to identify the existence of large particles, but involves a multiple step procedure and additional apparatus for filtering the sample.
Though there are always some analytical methods that are able to identify the existence of large particles, these methods are laboratory procedures requiring multi-step sample pretreatment, such as filtering, diluting, thermo-decomposition of oil samples, acidic-dissolving, solvent-washing, and so on. Apparently, these methods are disadvantaged for delayed report, resource-and-time consuming, and skill-demanding. It would be desirable to provide an apparatus that can conduct immediate analysis of a used oil sample while without missing large particles if there are any. Especially, it would be desirable to generate reports of the analysis on-site.
In addition, compared to emission spectroscopic apparatus based on laser or X-ray, a spark apparatus costs the least, and provides the most conventional and successful method for oil analysis. However, the requirement of continuous flow of sample fluid limits its application only to oil. Other chemicals servicing mechanical equipment, such as grease and coolant, possess equal importance of analysis of wear metals and have the same inhomogeneous issues caused by mixed or suspended particles. To date, even though one has invested a spark apparatus for on-site oil analysis, one still has to ship grease and coolant samples to a remote laboratory for analysis. It would be desirable to expand the usage of a spark apparatus to a plurality of forms of samples, such as grease, coolant, vessel fuel, and so on, in addition to oil.
It is understood that warming a viscous lubricant sample improves its excitation. It would be desirable to provide a means to heat-bath the sample before or during the excitation leading to emission spectroscopy.
Insofar as I am aware, the emission spectroscopy based on XRF and LIBS cannot provide a method to distinguish large particles from small ones without employing some kinds of sample-pretreatments, such as filtering and solvent-washing. In conclusion, there is a need to provide an improved method and apparatus to address the problems as set forth above, and for all types of atomic excitation approaches, including, but not limited to, spark, X-ray, and laser-induced-breakdown.